What age do chickens start to breed

I am pretty new to chickens. Mine are about 6 months old. I have 4 hens/4 roosters (from what I can tell so far).

My question is, when do Roosters and hens mature as far as trying to mate, breed, lay eggs. Right now I let them free range all day and they put themselves up at dusk. Of course I come out and hand feed them some treats each day too But I need to know when I should start to separate the roosters from the hens. Right now I only have 4 silkie hens & 1 Rooster that I would want to keep together. The other 3 roosters are different breeds (delaware, crele polish, buff laced polish) and what I'm saying is I don't want a bunch of mixed chicks popping up out of the blue in their barn.

What age do they mate with each other? What age should I start seeing eggs? I read on the net 1 year they will start to mate, but I saw my roo on top of a hen today so I was like uh oh 6 months early? Right now I'm just doing this as a hobby type thing, but I would like to maybe breed some chickens in the future - just not right now. I have some really pretty colored roosters and think they may make some pretty babies. I also heard you can not have too many roosters. I was hoping to have 1 rooster per breed. Does that seem ok or will they all still fight?

Oh and one more question - sorry guys! How do you keep the eggs from forming into babies? Just keep the male rooster separate at all times? Is this possible if they free range? Right now, I just let them out in the morning and let them run around my yard all day. They don't try to get out of the fence and even come when I call "here babies" for treats.

Like I said, I'm very new to this. I use to be a city girl in Detroit lol!! Since I moved to the country I have gotten into chickens and I think I'm addicted!

Mine started around 5 months and I had a nice hatch from my BCM's. Are you sure they are not laying eggs? They will lay in odd places outside. My white silkies started laying at 5 months too but I did not have a roo for them. I do now and I don't know if he has tried his thing yet. He's young.

I don't know. I really didn't think they would start laying other than their barn. I did hear my girl make some crazy loud bawks a couple different times during the day. I've watched some Youtube videos when one will lay an egg and announce it. I guess I should start checking around my property then huh!